1. Field of the Invention
In general, the present invention relates to television signals having Vertical Blanking Interval (VBI) data, and more particularly to the encoding and decoding of VBI data.
2. Statement of Related Art
In television broadcast systems, a television picture is referred to as a "raster." In the United States, a raster consists of 525 horizontal lines for video data sent over the course of two successive interlaced fields. These horizontal lines make up the full scope of the television screen. The horizontal lines are displayed in a receiving television set sequentially; however, they are displayed with such speed that a viewer sees only the complete picture, not the individual lines. The first several lines are said to be "blanked", and the time interval associated with these lines is referred to as the Vertical Blanking Interval (VBI). The VBI is essentially the portion of the television signal which carries no visual information and appears as a horizontal black bar between the pictures when a TV set needs vertical tuning. VBI lines are often used to transmit a variety of test and control signals as well as certain types of data. In particular, the VBI is used by the television set to determine where on the television screen the video signal should be displayed.
The VBI is often used to transmit digital data and test signals along with the audio and video signals. For instance, in the United States, the Federal Communications Commission has authorized the insertion of test, cue, control, reference, and program-related signals during the VBI. These signals may be used to control and monitor the performance of studios, networks, and transmitters; to provide reference signals for automatic control of receivers equipped with vertical interval reference (VIR) circuits; and to offer audible and visual program material ancillary to the standard television broadcast.
Although television broadcast systems which are in use today transmit analog signals, digital VBI data is essentially transmitted in serial bitstream format. This is accomplished by switching the analog television signal between high and low amplitude levels. The digital VBI data is provided at a frequency which is often an integer multiple of the horizontal line rate; the particular multiple used depends upon the VBI format being used (e.g., World System Text, North American Basic Text Standard, Vertical Interval Time Code, etc.). Digitized data can also be inserted into the VBI for transmission at rates greater than 100,000 bps. The data embedded in the VBI signal can then be retrieved from a standard cable or a satellite system by a receiver set. Software packages then allow subscribers instant access to the information and can be displayed in a number of formats.
Over recent years, a variety of services have made use of the VBI lines to transmit data including Close-Captioned for the hearing impaired, A. C. Nielsen program identification, videotext and teletext news services. In addition, information services such as stock market quotations and news offerings are now available via the VBI of a CATV signal. VBI signals are now widely used throughout the world. However, these services differ in the way that the VBI data is formatted. A number of format standards are used around the world. The type of VBI data format used generally depends upon the geographic region and the particular cable television service provider.
The fact that there are a number of different VBI format standards throughout the world is problematic since each VBI format standard requires configuration of the television broadcast system according to the particular format requirements for that VBI format. Particularly, for each VBI format, the television broadcast system requires configuration on the transmitting side and the receiving side. Television broadcasters must customize their transmission system according to the format requirements of a given geographic region or of a particular customer. Similarly the customer's receiving system must be configured for a particular VBI format. It is therefore desirable to have a single television broadcast system that is capable of handling VBI data regardless of its format.
For example, this need was recognized in McArthur, U.S. Pat. No. 5,555,025, which describes a circuit for decoding VBI television data having any one of a plurality of VBI formats. In the decoder, the controller receives the digitized television signal, the clock signal and a format signal from a host computer system indicating which VBI format is to be decoded. The controller generates a sample signal at the data frequency in response to the clock signal and the VBI format signal and causes a register to load VBI data at the midpoint in time of each bit of VBI data.
However, the McArthur patent is limiting in that the decoder requires information relating to the format of the data signal that it receives. The implementation of the decoder requires a host computer system which provides the decoder with the appropriate information relating to format of the data signal. As a result, information relating to the various data formats must be pre-programed into the host computer system. If a new data format was to be subsequently implemented, the host computer system would not have the necessary format information for the decoder to decode incoming data. Further, the McArthur patent does not teach an encoder that is capable of handling any number of VBI formats. In general, the McArthur patent fails to teach a television broadcast system that handles VBI data regardless of its format.
It is therefore an object of the present invention to provide a universal television communications system capable of transferring VBI data regardless of the VBI data format.
It is another object of the invention to provide an encoder and decoder that may be implemented to handle VBI data communication regardless of the VBI format being used.
A further object of the invention is to provide an encoder and a decoder that capable of respectively manipulating and de-manipulating VBI data to and from an arbitrary VBI format.
A further object of the invention is to provide an encoder and decoder that may be used for all data formats including those presently known as well as those that may be developed in the future.
Yet another object is to provide a method or apparatus of converting VBI data from a certain format to an arbitrary generic data format and reconverting the VBI data from the arbitrary generic format back to the previous data format.